From 2014 onwards, software which manipulated air pollution tests was discovered in vehicles from some car makers; the software recognized when the standardized emissions test was being done, and adjusted the engine to emit less during the test. The cars emitted much higher levels of pollution under real-world driving conditions. Some cars' emissions were higher even though there was no manipulated software. Since 2016, 38 out of 40 diesel cars tested by ADAC failed a NOx-test.